I just added Western Europe to mine about a week ago, I connected the unit to my computer, which opened the Garmin software (that I never use really, so forget what I did last time)

I cannot access my computer, but this time it was pretty straightforward, managing maps was intuitive, I could easily see that I had north america and Latin America also, so to free up space I got rid of the Latin America maps, and this freed up enough space to easily put Western Europe in (while still having north america)
It did not take that long to transfer Western Europe, maybe 20 mins? and it's been working fine here in Scotland.

A few years back when I did this, it seemed more complicated, and I had to remove the n America stuff to have room for the Europe stuff.
I must not have noticed the Latin America maps that time.

I'm sure it will work out for you